This invention has application to and great utility in connection with mine roof bolts, although its utility is not confined thereto. For purposes of illustration, the background of the invention will be described in connection with the roof bolting art. If a roof bolt is drawn too tight, the expansion end of the bolt will fracture the surrounding rock, not only loosening its grip but seriously weakening the roof structure. If the bolt is not drawn up tightly enough, it does not give the requisite support to the roof. After the roof bolt is installed, a roof bolt's tension may bleed off, to leave the roof structure largely unsupported, or if the roof structure fails, the bolt will be over-tensioned, leading to falls. Torque wrenches are commonly used to drive the nuts on roof bolts. However, burred or damaged threads or rust or other foreign material on or in the threads can produce false results, since the torque wrench is reading the turning torque or moment of the nut, and not the amount of tension in the shank of the roof bolt. Human error can also lead to over-torquing. Once the roof bolts are installed, there is now no simple way to test the amount of tension in the roof bolt.
One of the objects of this invention is to provide a safety device by which change in pressure between a stop on a shank anchored to a surface, and the surface, is indicated by sight, sound, or smell, or some combination of those.
Another object is to provide such a device and method for its use, which is simple, economical, and reliable.
Other objects will become apparent to those skilled in the art in the light of the following description and accompanying drawings.